(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and an apparatus and method for driving the same. More specifically, the present invention relates to an LCD having a multiframe inverting function, and an apparatus and method for driving the same.
(b) Description of the Related Art
As personal computers or televisions have recently become more light-weighted and thinner, LCDs are required to have smaller weight and thickness. For this reason, flat panel type display devices such as LCD are used as a substitute for a cathode ray tube (CRT) and put to practical uses in various applications.
LCD is a display device in which electric field is supplied to a liquid crystal material having an anisotropic dielectric constant between two substrates and controlled to regulate the amount of light passing through the substrates, thereby generating a desired image signal.
LCD is a representative of portable flat-panel type display devices, among which TFT (Thin Film Transistor)-LCD using an array of TFTs as a switching element is most widely used.
Typically, LCD includes a plurality of gate lines for transmitting a scanning signal, a plurality of data lines intersecting the gate lines and transmitting image data, and a plurality of pixels each formed at a region surrounded by the gate lines and the data lines and connected to the gate lines and the data lines via switching elements in the matrix form.
In the LCD, image data are supplied to the individual pixels as follows.
First, a gate-on signal, i.e., scanning signal is sequentially supplied to the gate lines to turn on the switching elements connected to the gate lines in sequence and, simultaneously, to provide image signals to be supplied to pixel rows corresponding to the gate lines, i.e., supply a gradation voltage to the respective data lines. The image signals supplied to the data lines are supplied to the individual pixels via the switching elements turned on. The gate-on signal is sequentially supplied to all gate lines for one frame so as to display an image of one frame.
It is necessary to invert the gradation voltage with respect to a common voltage, because of the problematic characteristic of the liquid crystal material that the liquid crystal material is degraded under the electric field continuously supplied in one direction. Namely, when a signal voltage positive in polarity is supplied to a pixel, a negative signal voltage has to be supplied to the next frame.
For this purpose, the TFT-LCD is inverted on a frame-by-frame basis (in the frame inversion method (FIM)), on a line-by-line basis (in the line inversion method (LIM)), on a column-by-column basis (in the column inversion method (CIM)), or on a pixel-by-pixel basis (in the dot inversion method (DIM)).
These inversion methods make use of the fact that the averaged brightness of the individual dots in a given area is constant because the human eyes recognize different dots at the same time. The methods are so effective in general displays as not to make the users feel inconvenient, but flickering occurs when displaying the same patterns as the inversion methods. Flickering refers to a quality-related characteristic of the picture that appears in the presence of a transmittivity difference between the two polarities in periodically switching the charging polarity of liquid crystals between positive (+) and negative (−) polarities. Flickering occurs when the same voltage cannot be supplied to the individual dots due to RC delay that depends on the length of the panel, because the individual dots are distributed in area and a control voltage for each dot is supplied in one direction.
That is, flickering occurs in the horizontal pattern for line inversion, in the vertical pattern for column inversion, and in the dot pattern for dot inversion, because human eyes recognize these patterns in the same way as the pattern in frame inversion.
It is however still problematic in that the horizontal, vertical and dot patterns are all included in the range of the user screen.
In an attempt to overcome this problem, there is suggested the 2×1 dot inversion method as illustrated in FIG. 2, in which positive (+) and negative (−) voltages are viewed in a pattern included in the range of the user screen to reduce flickering. This method eliminates flickering from all user screens because the user scarcely uses the 2×1 dot screen that shows flickering. The 2×1 dot inversion method may drive the LCD module with the flickering a lot less noticed, but creates blurred horizontal lines in the screen due to a difference in the charging rate between the odd and even lines.
For example, when the data voltage wavelength is input in the form of pulses with a four-line period, the head of the waveform is delayed due to resistance and capacitance of the data lines, which leads to a delay of the pixel voltage corresponding to the odd lines.
The pixel voltage corresponding to the even lines is also delayed in the next frame for the same reason except that the voltage is in a low state.
The reasons why the head of the waveform is delayed are also considered as that the gate waveform is recognized differently from even lines to odd lines in correlation with data when the waveform varies due to the RC delay of the gate lines, and that the pixel voltage at the head of the waveform differs from odd lines to even lines in connecting an auxiliary capacitance Cst to the gate of the head to drive the auxiliary capacitance.
For these reasons, horizontal lines are created in displaying a screen with an intermediate gradation brightness, which eventually deteriorates the quality of the image.